THE APPLICATION OF MULTIVARIATE STATISTICAL TECHNIQUES TO DOMESTIC WELL MONITORING DATA TO ASSESS IMPACTS FROM SEPTIC EFFLUENT DISCHARGE WITHIN A COASTAL DUNE COMPLEX, NORTHERN INDIANA

Potential contamination of groundwater and surface water from the discharge of septic effluent was identified by the National Park Service and the Indiana State Department of Health as a concern in the Town of Beverly Shores, located on Lake Michigan within the Indiana Dunes National Lakeshore. The approximately 1,000 residents of the town rely on individual septic systems as their means for domestic wastewater disposal and on residential wells as their water source. The highly permeable dune-sand soils and generally shallow groundwater with short flow paths to surface waters (including the Lake Michigan beaches) are conducive to transport of pollution through the release of household wastewater from septic systems to the environment.

In an effort to evaluate the degree and extent of local groundwater contamination from septic-effluent discharge, two rounds of sampling of domestic water-supply wells for indicator parameters (coliform bacteria, nitrate, ammonia, chloride, sulfate, electrical conductivity, pH, dissolved oxygen, and detergent surfactants) at about 70 residences were undertaken in the autumn and spring of a single water year. An analysis of those data indicates that areas of noticeable, but limited, impacts from septic effluent exist in the town and that they are generally associated with the more highly developed areas. Exceedances of health-related drinking-water standards for coliform bacteria and nitrate were localized, suggesting failure of some septic systems. Multivariate statistical analyses of the data suggest that higher septic-system density, thinner unsaturated zones, and the use of water treatment systems increase the impacts on groundwater quality from septic-effluent discharge.